The anxiety is understandable, young kids, a life threatening disease hopefully gone, some seriously toxic treatments with damage potential, and some real unknowns.
I would not dismiss the "not well" parts, nor despair either, there are a number of "benign disease" possibilities. This is the way chronically ill people often are, where common medical tests seem "ok" but they have pain and/or other seriously debilitating problems that go on (and on) until they are addressed, if ever. Conventional medicine is not good at surfacing many digestive issues, even the ones just sitting there in some 20 lb postgraduate GI textbook. Biologically oriented CAM practitioners (ND, MD, DO, DABCI, NP) may have a better batting average on some things, because they invested time and effort on a broader sweep.
I'll give one easy example. Celiac disease is a severe form of digestive disease, yet the average time to diagnosis is nine years, of the few percent that
are ever diagnosed, from patients commonly dismissed as psychiatric cases. Many celiac patients have run through 1-2 dozen doctors without recognition. Other problems are emergent, like NAFLD.
... More recently, it has become appreciated that all the chemotherapy agents used in colorectal cancer appear capable of causing steatosis. (I am not saying you have this, but rather that post chemo problems have been underappreciated, inadequately discussed and analyzed)